#include<stdio.h>

void to_binary(unsigned long);

int main(void)
{
    unsigned long number;
    printf("Enter an integer (q to quit): \n");
    while(scanf("%ul",&number)==1)
    {
        printf("Binary equivalent: ");
        to_binary(number);
        putchar('\n');
        printf("Enter an integer (q to quit): \n");
    }
    printf("Done.\n");

    return 0;
}

void to_binary(unsigned long n)
{
    int r;
    r=n%2;
    if(n>=2)
        to_binary(n/2);
    putchar('0'+r);

    return; 
}
